title: A fungal endophyte induces transcription of genes encoding a redundant fungicide pathway in its host plant.
abstract: BACKGROUND
  Taxol is an anti-cancer drug harvested from Taxus trees, proposed ecologically to act as a fungicide. Taxus is host to fungal endophytes, defined as organisms that inhabit plants without causing disease. The Taxus endophytes have been shown to synthesize Taxol in vitro, providing Taxus with a second potential biosynthetic route for this protective metabolite. Taxol levels in plants vary 125-fold between individual trees, but the underlying reason has remained unknown.
  
  
  RESULTS
  Comparing Taxus trees or branches within a tree, correlations were observed between Taxol content, and quantity of its resident Taxol-producing endophyte, Paraconiothyrium SSM001. Depletion of fungal endophyte in planta by fungicide reduced plant Taxol accumulation. Fungicide treatment of intact plants caused concomitant decreases in transcript and/or protein levels corresponding to two critical genes required for plant Taxol biosynthesis. Taxol showed fungicidal activity against fungal pathogens of conifer wood, the natural habitat of the Taxol-producing endophyte. Consistent with other Taxol-producing endophytes, SSM001 was resistant to Taxol.
  
  
  CONCLUSIONS
  These results suggest that the variation in Taxol content between intact Taxus plants and/or tissues is at least in part caused by varying degrees of transcriptional elicitation of plant Taxol biosynthetic genes by its Taxol-producing endophyte. As Taxol is a fungicide, and the endophyte is resistant to Taxol, we discuss how this endophyte strategy may be to prevent colonization by its fungal competitors but at minimal metabolic cost to itself.
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON N1G 2W1, Canada.
authors.forename: Sameh S M
authors.initials: SS
authors.lastname: Soliman
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Trobacher
authors.forename: Rong
authors.initials: R
authors.lastname: Tsao
authors.forename: John S
authors.initials: JS
authors.lastname: Greenwood
authors.forename: Manish N
authors.initials: MN
authors.lastname: Raizada
mesh_terms: D001203:Ascomycota / Q000502:physiology*; D060026:Endophytes / Q000502:physiology*; D005659:Fungicides, Industrial / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D054884:Host-Pathogen Interactions; D017239:Paclitaxel / Q000096:biosynthesis*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D020946:Taxus / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology*; D014158:Transcription, Genetic; D015854:Up-Regulation
chemical_list: D005659:Fungicides, Industrial; D010940:Plant Proteins; D017239:Paclitaxel